This epidemiologic study will extend observation on 30,000 former students at Harvard to identify patterns of physical activity conducive to the avoidance of heart attacks in middle and later life. Prospective observations will utilize both historical and ongoing perspectives to test competing hypotheses of the role of exercise in coronary heart disease prevention, i.e., whether benefit derives from overall energy output or from achievement of a burst of high output for certain periods of time. Patterns of exertion favoring coronary well-being in successive age groups ranging 40-80 years will be studied. Mail questionnaires will be used to log, in diary form, physical activity during a 48-hour period of working and leisure time (a successive Friday and Saturday). These findings will supplement data already compiled from college physical examination records (1916-1950) and followup questionnaires (1962 or 1966 and 1972). Further inquiries will ascertain nonfatal heart attacks, while an existing mechanism will report fatal events.